The present invention relates to methods and compositions for sequestering metal ions in solution, and to methods and compositions for combating metal compound deposits. Of particular interest (but not the exclusive interest) is the prevention of the deleterious effects associated with compounds of alkaline earth metals. Calcium salts, for example calcium carbonate, and magnesium salts form particularly prevalent salt deposits commonly known as scale or lime scale, which is troublesome in itself and which provides sites for concentrations of soils and bacterial growth. Calcium and magnesium ions in aqueous solution are responsible for xe2x80x9chardxe2x80x9d water, in which it is difficult to form a lather with soap or detergent, and which may then form an unpleasant scum. Of course, it is from hard water that scale forms.
Known calcium ion sequestrants, acting as water softeners, include sodium carbonate, sodium citrate, and phosphates, including sodium acid pyrophosphate, sodium polyphosphate, trisodium phosphate, tetrasodium pyrophosphate and sodium tripolyphosphate. Many such sequestrants have certain limitations on how they can be used, for example within a certain pH range only, some give rise to undesirable effluents, and some are corrosive to metals.
It would be desirable to employ a composition which can act as an effective sequestrant, acting as a water softener, without having one or more of the problems of known sequestrants, as mentioned above.
Known scale removers typically employ mineral acids, for example hydrochloric acid. They must be employed with some care and may represent an environmental hazard, and be corrosive to metals.
It would be desirable to employ a composition which can effectively combat solid metal compound deposits, for example scale, without incurring one or more of the problems of known compounds, as mentioned above.
In accordance with a first aspect of the present invention there is provided a method of combating metal species carried by or deposited from water, the method comprising the delivery to an environment in which the metal species are present of a composition comprising an algin.
The term xe2x80x9ccombatingxe2x80x9d may include the treatment of a metal compound already present as a solid deposit, or the treatment of the said environment to prevent or hinder the deposition of such a compound from solution, or both. Thus, the treatment could be one of deposit removal, and/or water purification and/or water softening.
The term xe2x80x9cmetal speciesxe2x80x9d includes ions in solution and deposits of metal compounds, including metal oxides and, especially, metal salts.
Algins may be found in and isolated from various organisms, in particular from algae belonging to the order Phaeophyceae and soil bacteria such as Azotobacter vinelandii and Azotobacter crococcum and from several strains of Pseudomonas bacteria. Common algal sources of algins include Laminaria digitata, Ecklonia maxima, Macrocystis pyrifera, Lessonia nigrescens, Ascophyllum nodosum, Laminaria japonica, Durvillea antartica, Durvillea potatorum and, especially, Laminaria hyperborea. 
Alginic acid is a linear hetero-polysaccharide comprising units of xcex2-D-mannuronic acid and xcex1-L-guluronic acid. Alginic acid may comprise homopolymeric sequences of mannuronic acid, homopolymeric sequences of guluronic acid, and mixed sequences of mannuronic acid and guluronic acid units.
Alginic acid itself is effective in the method of the present invention in combating metal species. Salts of alginic acid used in the method of the present invention may include alkali metal salts, for example sodium and potassium salts, and ammonium and alkanolamine salts. Alkali metal salts are of particular interest.
The term xe2x80x9calginsxe2x80x9d as used herein includes alginic acid and salts of alginic acid, irrespective of the relative proportion of mannuronic and guluronic units, and is intended to include glycolated or alkoxylated derivatives, especially those derivatized with propylene glycol. However, preferred compounds are not alkoxylated or glycolated. Guluronic acid-rich alginic acid and guluronic acid-rich salts of alginic acid are of particular interest. Preferred compounds have at least about 50%, more preferably about 55-99%, most preferably about 60-80% of guluronic units (by weight), the balance being mannuronic units. For guidance on production of algins very high in guluronic units the reader is referred to International Patent Application Publication WO 98/51710.
We have found particularly good results, notably in removing metal compound deposits, using methods which employ algins and an acid (by which we mean a non-alginic acid, when said algin is alginic acid). Particularly preferred are methods which employ a salt of alginic acid, preferably an alkali metal alginate, and an acid.
In such compositions said acid could (except when said algin is itself alginic acid) be alginic acid. However good results may be obtained using a salt of alginic acid and an acid which is not alginic acid. Suitably, such an acid is an organic acid, preferably a carboxylic acid, preferably one having a plurality of carboxylic groups, for example citric acid, or gluconic acid. Preferably the algin can dissolve in water before the pH is substantially reduced. Gluconic acid can be produced by cleavage of glucono delta lactone in the presence of water. This takes place slowly and offers the possibility of a dry mix of ingredients, including the algin and glucono delta lactone (or other suitable lactone, splitting in the presence of water to form an acid, preferably once the algin has dissolved). Alternatively, the acid could be a mineral acid, for example hydrochloric acid, preferably present in low concentration, and preferably added after the algin has dissolved. Preferably, a non-alginic acid employed in this invention is substantially odorless.
While an acid could be employed in a method of combating a metal species before or after a salt of alginic acid is employed, preferably both such compounds are used at the same time. To this end, a treatment composition may comprise both such compounds in admixture, preferably in an aqueous composition.
Very good results may be obtained, notably in methods of removing metal salt deposits, when the algin is sodium alginate. Especially preferred, however, is potassium alginate. Potassium alginate appears from our tests to be relatively easy to incorporate in stable solutions and to be highly effective in removal of deposits of metal compounds.
Especially preferred for use in methods of water softening is an alginic acid, preferably as the sole algin present.
Preferably, the pH of an aqueous composition comprising an algin is in a range of about 2-12, preferably about 3-11.
Preferably, the pH of an aqueous composition comprising an algin and an acid is less than about 7, preferably about 2-6, and most preferably about 3-5. Preferably, the pH of the composition is in excess of the pKa value of the algin. As noted above, we have found that formation of a stable solution is most easily achieved when the algin is mixed in (preferably dissolved in) water, which is then acidified by an acid.
On the alkaline side, we have obtained good results at pH values in a range of about 8.5-11, especially about 9-10.5, as would be found in dishwashing machines.
A composition used in the method could be provided in a solid form, for example a powder or granules, which is applied directly to a metal compound deposit to be combated or to a substrate on which the deposit could form, or added to water with which the deposit or a said substrate is in contact, or which otherwise contains deleterious or potentially deleterious metal ions. It could be a tablet to be added to, for example, a cistern of a lavatory. Preferably, however, the composition is provided in a liquid form, preferably as an aqueous composition. The in-use composition will suitably be made by dilution of a concentrate, for example a powder, granules or tablet; or a gel or liquid concentrate, with the algin being provided in a pre-hydrated form.
When alginic acid is employed in an aqueous composition, the aqueous composition suitably comprises at least about 0.001 wt % alginic acid, preferably at least about 0.01 wt %, preferably at least about 0.05 wt %, and most preferably at least about 0.1 wt %. Suitably, it comprises up to about 5 wt % alginic acid, preferably up to about 1 wt %, more preferably up to about 0.5 wt %.
When a salt of alginic acid is employed in an aqueous composition, the aqueous composition suitably comprises at least about 0.001 wt % thereof, preferably at least about 0.01 wt %, more preferably at least about 0.05 wt %, and most preferably at least about 0.1 wt %. Suitably, it comprises up to about 5 wt % thereof, preferably up to about 1 wt %, more preferably up to about 0.5 wt %.
In aqueous compositions which contain an algin and an acid which is not alginic acid the definitions given above apply to the algin, and the acid is preferably present in an amount to provide a composition of pH as required; preferably within the parameters stated above for pH.
In aqueous compositions which contain both alginic acid and a salt of alginic acid the above definitions apply to each such component. Preferably, however, such compositions comprise at least about 0.02 wt % of the alginic acid and the alginic salt in combination, more preferably at least about 0.05 wt %, and most preferably at least about 0.1 wt %. Preferably, the composition comprises up to about 5 wt % of the alginic acid and the alginic salt in combination, more preferably up to about 1 wt %, most preferably up to about 0.5 wt %.
In compositions which contain alginic acid and a salt of alginic acid there is suitably at least about 1 part acid to about 5 parts of the salt, by weight, and preferably at least about 1 part acid to about 3 parts of the salt, by weight. More preferably, there is at least about 2 parts acid to about 3 parts of the salt, by weight, and most preferably at least about 1 part acid to about 1 part salt, by weight. Preferably, there is up to about 10 parts acid to about 1 part of the salt, by weight, and more preferably up to about 5 parts acid to about 1 part of the salt, by weight.
Liquid compositions containing certain (generally higher) concentrations of an algin may need to employ solvating or dispersal agents and/or be pumped to the site of the application. A liquid composition as defined above is preferably a ready-for-use composition, to be applied by a customer to a deposit or to water in contact with a deposit or otherwise delivered to an environment prone to such deposits (for example hard water). In use the concentration of the algin(s) may thus be reduced from the values stated above by water present in the environment of the deposit.
A composition may, in addition to the algin, contain one or more additional components, for example selected from biocides, preservatives, bleaching agents, sanitizing agents, fillers, enzymes, colorants, hydrotropes, surfactants (for example anionic, non-ionic, cationic and amphoteric surfactants compatible with the algin, and of which anionic and non-ionic surfactants are preferred), perfumants and suspending agents, for example gum or starch suspending agents. Especially preferred as a bleaching and/or sanitizing agent is a phthalimido-peroxy carboxylic acid in adduct form with a cyclodextrin, as described in European published patent application EP-A-895777, the contents of which are hereinafter incorporated by reference. A preferred material of this type is xcex2-cyclodextrin complexed with epsilon-phthalimido peroxyhexanoic acid. As an alternative bleaching agent sodium chlorite could be used, when the pH of the composition is such that chlorine dioxide will be released. The sodium chlorite may need to be added from a second compartment whereas the phthalimido-peroxycarboxylic acid/cyclodextrin adduct may be co-formulated with the algin.
A suitable anionic surfactant is an anionic organic surfactant, which is usually employed in a soluble salt form, preferably as an alkali metal salt, especially as a sodium salt. Although other types of anionic detergents may be utilized, such as higher fatty acyl sarcosides, alkyl sulphosuccinates, alkyl ether sulphosuccinates, alkylamide sulphosuccinates, alkyl sulphosuccinates, alkyl sulphoacetates, alkyl phosphates, alkyl ether phosphates, acyl isothionates, N-acyl taurates and acyl lactylates, or conventional xe2x80x9csoapsxe2x80x9d of fatty acids, the preferred anionic surfactants employed are those which are described as being of a sulphonate or sulphate type. These include linear higher alkylaryl sulphonates (for example alkylbenzene sulphonates), alkyl sulphates, alkyl ether sulphates, alkylamidoether sulphates, alkylarylpolyether sulphates, monoglyceride sulphates, alkyl sulphonates, alkylamido sulphonates, higher fatty alcohol sulphates, higher fatty alcohol polyalkoxylate sulphates, olefin sulphonates, xcex1-methyl ester sulphonates and paraffin sulphonates. An extensive listing of anionic detergents, including such sulph(on)ate surfactants, is given at pages 25 to 138 of the text Surface Active Agents and Detergents, Vol. II, by Schwartz, Perry and Berch, Interscience Publishers, Inc. (1958), which is incorporated herein by reference. Usually, the higher alkyl group of such anionic surfactants has 8 to 24 carbon atoms, especially 10 to 20 carbon atoms, preferably 12 to 18 carbon atoms, and the alkoxylate content of such anionic surfactants that are alkoxylated (preferably ethoxylated or ethoxylated/propoxylated) is in the range of 1 to 4 alkoxy groups per mole.
One preferred class of anionic surfactants comprises the alkali metal (preferably sodium) alkyl sulphates, preferably having linear C12-18 alkyl groups. Another preferred class of anionic surfactants comprises alkali metal (preferably sodium) alkylaryl sulphonates (especially alkylbenzene sulphonates), preferably having linear C10-13 alkyl groups.
A suitable non-ionic surfactant of an algin-containing composition is a condensation product of a higher fatty alcohol or alkyl phenol with a lower alkylene oxide, such as ethylene oxide or a mixture of ethylene oxide and propylene oxide. In such non-ionic surfactants the higher fatty moiety will normally be of 7 to 16 carbon atoms and there will usually be present from 3 to 20, preferably 4 to 15 moles of alkylene oxide per mole of higher fatty alcohol. Another class of non-ionic surfactants that could be used is sorbitan esters of fatty acids having from 10 to 24 carbon atoms, for example sorbitan mono-oleate.
The cleaning composition used in a machine washing method hereof may contain a builder. Suitable builders include water-soluble inorganic salt builders, preferably sodium salts, such as sodium polyphosphates, e.g., sodium tripolyphosphate and sodium pyrophosphate, sodium carbonate, sodium bicarbonate, sodium sesquicarbonate, sodium silicate, sodium disilicate, sodium metasilicate and sodium borate. In addition to the water-soluble inorganic salts, water insoluble builders may also be useful, including the ion exchanging zeolites, such as Zeolite 4A. Organic builders may also be employed. Among suitable organic builders are polyacetal carboxylates, as described in U.S. Pat. No. 4,725,455, and water soluble salts of lower hydroxycarboxylic acids, such as sodium citrate and sodium gluconate.
In certain preventive methods of the invention a liquid composition is a relatively viscous composition, such that it may cling to a substrate which has a vertical or inclined surface.
In certain methods of the invention to combat a deposit already present, a liquid composition may be relatively non-viscous, for example free-running. Such a composition may run off regions of a substrate not bearing a deposit but bind to (for example form a gel with) a deposit on the substrate, even when the surface is vertical or inclined. Thus, it may also have a disclosing function, enabling a user to see when the deposit is present. To facilitate this, it may contain a colorant which contrasts with the substrate (for example sanitary ware). It may alternatively have a cosmetic function, to cling to a deposit and mask it from view. To this end a composition of the invention may contain a colorant to match the color of the substrate. For example, it may contain a white colorant or opacifier, when intended for use on white sanitary ware.
When a colorant is used with a phthalimido-peroxycarboxylic acid/cyclodextrin bleaching/sanitizing agent as described above, we have found that the composition retains its color prior to use. When applied to a deposit in an aqueous environment it clings, with the algin, to the scale, which is therefore disclosed by the color. However, color is gradually lost, as scale is removed. Thus, we conclude that bound to the deposit is a complex comprising the algin (or its anions), the colorant and the bleaching agent.
The invention may be used in a domestic or industrial environment.
The method of the invention may be applied to water softening and/or purifying, for example in drinking water filters, washing machines for fabrics, dishwashing machines, kettles, irons and boilers; to cosmetics; and to cleaning products, for example teeth and denture cleaners, bathroom tile and shower screen cleaners, window cleaners, car cleaners, lavatory cleaners, dish- and fabric-washing powders and liquids, soaps, detergents, and shampoos. An advantage of the present invention is that the compositions can be non-corrosive to metals, unlike certain compositions used heretofore.
In the application of one aspect of the method a deposit which is combated is typically already carried as a surface deposit on a substrate, for example a ceramic item such as a sanitary ware product, or a metallic item such as a pipe, kettle, iron, boiler or heater element.
In other applications the method could be applied to the treatment of existing deposits and/or the prevention of deposits in oilfield or oil processing environments, for example in pumping equipment and pipelines.
In other applications the method could be applied in the purification of water to yield improved drinking water.
In the application of another aspect of the method it is a machine washing process, preferably of fabrics, and the composition softens the washing water and prevents deposition of scale or other metal compounds, by sequestering metal ions from the wash water. Suitably, the composition is added at the start of the wash cycle. While, like the known sequestrants mentioned above, it may be formulated to be washed away, in a preferred method it is present throughout the washing operation, including the rinse cycle. This can be achieved by providing the composition within a water-permeable container, such that the algin, and the complex it forms when it captures the metal ions, is unable to pass through the walls of the water-permeable container. The container could be a rigid item with microporous openings in its wall(s), but it is preferably a bag (by which we include a pouch or sachet). The bag may suitably have textile, paper or polymeric walls. Polymeric walls may be of a membrane formed by extrusion or film casting, and have micropores. Walls of non-woven fibrous materials are particularly suitable.
Water-porous containers containing an algin represent a second aspect of the present invention. Thus, in accordance with a second aspect of the invention there is provided a container containing an algin, the container being permeable to water but impermeable to alginic species.
In other applications the method of the invention may be applied as part of a manual cleaning method. The algin is preferably added to washing water at or before the start of cleaning. Preferably, it remains within the washing water throughout the cleaning method. During the cleaning method it may suitably be retained in a container of the type described above. By capturing metal ions, particularly calcium ions, any cleaning agent present in the water is able to work more effectively, and/or surfaces in contact with the washing water are soiled less, whether by encrustations or by water marks (xe2x80x9cspottingxe2x80x9d) left when droplets on the surfaces evaporate. For example, an algin can be used in a bath to soften the bath water, improve lathering and reduce scum formation and settlement on the bath; or in the water used for cleaning windows or washing a car to soften the wash water and reduce xe2x80x9cspotting.xe2x80x9d
A method of the invention is suitably carried out at a temperature in a range of about 5 to about 100xc2x0 C., especially about 10 to about 60xc2x0 C. Scale removal variants of the invention are preferably carried out at a temperature of about 10 to about 30xc2x0 C., more preferably about 15 to about 30xc2x0 C., and most conveniently at ambient temperature. Water softening variants of the invention are preferably carried out at a temperature of about 10 to about 100xc2x0 C., or higher under applied pressure; but preferably about 20 to about 60xc2x0 C.
A deposit or substrate on which a deposit may form is suitably subjected to the algin in an aqueous medium for a soak period, preferably at least about 1 minute, preferably at least about 5 minutes, more preferably at least about 10 minutes, still more preferably at least about 15 minutes, yet more preferably at least about 1 hour, and most preferably for at least about 6 hours; and commonly overnight in many practical situations. However, we have found good results in experiments which treated deposits with an algin for 1 and 10 minutes, and for times in between.
In accordance with a third aspect of the present invention there is provided a method of treating a deposit of a metal compound, the method comprising the application to the deposit of a composition comprising an algin.
In accordance with a fourth aspect of the present invention there is provided a method of preventing the deposition of a metal compound from an aqueous environment, the method comprising the inclusion in the aqueous environment of a composition comprising an algin.
In accordance with a fifth aspect of the present invention there is provided a method of purifying and/or softening water, the method comprising the inclusion in the water of a composition comprising an algin.
The composition used is preferably such that it does not corrode or otherwise degrade metallic, plastic or ceramic surfaces.
The species combated may be ions and/or compounds of lead, copper or iron, or of alkaline earth metals, notably of strontium, barium, magnesium and, especially, calcium. Barium salt deposition is a significant problem in oilfield engineering, and magnesium and, especially, calcium salt deposition is a significant problem in situations in which hard water is employed. Copper and iron compounds may form unsightly deposits and lead species in water are detrimental to health. Most preferably, the methods of the invention are effective in combating calcium species.
In accordance with a sixth aspect of the invention there is provided an aqueous composition comprising an acid and a salt of alginic acid. Such a composition is preferably as defined above. The acid may be alginic acid. Preferably, the acid is an organic acid which is not alginic acid, for example citric acid. Preferably, the pH of the composition is as defined above.
In accordance with a seventh aspect of the present invention there is provided an aqueous composition comprising an algin, the composition being alkaline; its pH preferably being in a range of about 8.5-11.